Vacuum Distillation

Summary

In this video, Lisa Nichols demonstrates how to perform a vacuum distillation, a technique used to purify substances with high boiling points. By reducing the pressure, the boiling point of the substance is lowered, preventing decomposition. The setup involves a variety of equipment, including a heating mantle, stir bar, vacuum pump, and specialized glassware such as a claisen adapter and short path distillation apparatus. Lisa explains the steps to assemble the apparatus, control bumping during distillation, and safely finish the process by cooling the system before reintroducing air. The video offers a clear, detailed guide for performing distillation under vacuum.

Takeaways

• 😀 Vacuum distillation is used to purify substances with very high boiling points (e.g., 150°C or higher), reducing the chance of decomposition.
• 😀 Distilling under reduced pressure lowers the boiling point of the substance, allowing it to be purified at a safer, lower temperature.
• 😀 Always perform vacuum distillation in a fume hood for safety, as working under vacuum can be hazardous.
• 😀 Use a heating mantle to heat the mixture, and a stir bar for bump protection, as boiling chips don’t work under vacuum.
• 😀 A Claisen adapter is essential in vacuum distillation to prevent bumps or mini explosions in the flask during heating.
• 😀 Grease the joints of glassware to ensure an airtight seal, which is crucial for maintaining a vacuum system.
• 😀 For small-scale distillation, a short-path distillation apparatus is preferred as it minimizes the number of joints and ensures a better vacuum.
• 😀 Ensure the condenser hoses are properly connected and that the short path apparatus is securely attached to the ring stand with a clamp.
• 😀 Always use a thermometer with a ground glass joint, and place it in the correct spot in the distillation setup to monitor boiling temperature.
• 😀 Lower the pressure inside the system with the vacuum pump, and be cautious of bubbles that may form from low boiling impurities.
• 😀 Never allow a distillation flask to go dry. Always keep track of the liquid to avoid overheating or damaging the apparatus.
• 😀 When stopping the distillation, cool the system down first before releasing the vacuum to avoid sudden pressure changes that could damage the apparatus.

Q & A

What is the purpose of using a vacuum distillation?

Vacuum distillation is used to purify substances with high boiling points (e.g., over 150°C). By lowering the pressure, it reduces the boiling point of the substance, allowing distillation at lower temperatures and preventing decomposition.

Why is it necessary to work in a fume hood when conducting vacuum distillation?

Working in a fume hood ensures safety when performing vacuum distillation, as it provides a controlled and protected environment in case of accidents such as implosions or the release of hazardous vapors.

Why should a stir bar be used instead of boiling chips during vacuum distillation?

Boiling chips do not work under vacuum conditions because they may cause uneven boiling or bumping. A stir bar ensures smooth and controlled boiling by continuously stirring the liquid.

What is the role of the Claisen adapter in vacuum distillation?

The Claisen adapter prevents bumps, which are small explosions that can occur during distillation, by providing a controlled path for the liquid. It ensures that if bumping happens, it doesn’t affect the distillation process or contaminate the sample.

How should glassware joints be prepared for vacuum distillation?

Glassware joints should be greased with a small amount of grease to ensure an airtight seal. This is crucial for maintaining the vacuum and preventing atmospheric leakage during the distillation.

What is the advantage of using a short-path distillation apparatus for small amounts of liquid?

Short-path distillation apparatus is compact and fused, reducing the number of joints, which minimizes the risk of leaks. It is ideal for small quantities of liquid, as it provides an efficient setup with fewer connections.

What is the importance of the thermometer in the distillation setup?

The thermometer is crucial for monitoring the boiling point of the substance during the distillation process. It helps determine when the distillation is occurring at the desired temperature and is especially necessary when using short-path distillation.

What should you do if your distillation setup starts to bubble excessively?

Excessive bubbling, or bumping, can be controlled by adjusting the heat or lowering the stir plate. The Claisen adapter will contain the bumps, but if needed, you can reduce the heat using a lab jack to prevent the sample from boiling too aggressively.

Why is it important to never distill a flask to dryness?

Distilling to dryness can cause the sample to overheat or lead to the breakdown of materials. It's important to always leave some liquid in the flask to prevent any damage to the system or loss of distillate.

What safety precautions should be taken when shutting down the vacuum distillation process?

When stopping the distillation, it is crucial to first cool down the system by lowering the heat and using water to cool the distilling flask. Only then should you reintroduce air to the system, ensuring the pressure is safely equalized before turning off the vacuum.